1. Field of the Invention
The present invention broadly relates to a method for the selective removal of an oxide of carbon from a gas stream containing the same and an elemental halogen. In accordance with a particularly preferred embodiment, the invention provides a method for the selective removal of CO.sub.2 from a gas stream containing the same and fluorine, which stream is obtained from a high-power, pulsed, chemical DF laser.
2. Description of the Prior Art
It is well known that carbon dioxide is readily removable from substantially inert gas streams by various methods. For example, the removal of carbon dioxide from a gas stream by reaction with a base is well known, as is the use of a molecular sieve for effecting such separation. Methods also have been suggested for the separation of weak acids such as H.sub.2 S from gas streams containing the same and CO.sub.2 by utilizing an absorbent which preferentially removes the H.sub.2 S along with only a minor amount of CO.sub.2.
The removal of carbon dioxide from a gas stream containing the same and a halogen presents a very difficult problem. More particularly, the halogens, and fluorine in particular, are the more reactive elements known whereas CO.sub.2 is relatively inert. To the best of the inventor's knowledge, no expedient method for the selective removal of CO.sub.2 from a fluorine-containing gas exists, though the need for such a method does exist for use in conjunction with a pulsed chemical deuterium fluoride (DF) laser.
In a pulsed DF laser, molecular fluorine is dissociated by a suitable energy source such as flash photolysis or an electron beam into atomic fluorine as exemplified by the following equation: ##EQU1##
The atomic fluorine (F) then is reacted with deuteurium to produce the lasing species, vibrationally excited DF* which lases at a wavelength of about 3.8 .mu.m, as exemplified by the following equation: EQU F+D.sub.2 .fwdarw.DF*+D
Typically, the gas utilized in a pulsed DF laser comprises about 95% helium as a diluent and the balance will include a four-fold excess of F.sub.2 over D.sub.2. To maintain a high efficiency and minimize the inventory of stored gas required for operation of the laser it is necessary to remove the ground state deuterium fluoride formed during lasing. Removal of the DF is accomplished in a suitable scrubber, typically one containing activated sodium fluoride. The remaining helium diluent and the unused fluorine are recycled to the laser.
A particular advantage of a DF laser is its dual wavelength capability. Specifically, it has been found that excited DF can efficiently transfer its energy to CO.sub.2 which can lase at a wavelength of 10.6 .mu.m. Thus, the laser can be operated either on the DF or the CO.sub.2 lines. An important requirement for dual wavelength operation, however, is the ability to switch from one mode to the other without sacrificing the advantages gained by the gas recirculation. Since switching from CO.sub.2 lasing to DF lasing requires removal of the CO.sub.2, an effective method for the selective removal of CO.sub.2 from the fluorine-containing gas stream is essential.